1. Field of the Invention
The present invention relates to a printer and a method of controlling the same.
2. Related Art
Various kinds of motors, such as a sheet conveying motor for driving a conveying roller that conveys a printing sheet and a carriage motor for driving a carriage mounting a printing head, are provided in a printer. As these motors, DC motors are widely used because the DC motors generate little noises. A printer provided with a DC motor has an encoder including a scale, which has marks or slits arranged at prescribed distances therebetween in order to control position, speed, and the like of the DC motor, and a detector that detects the marks or slits of the scale and outputs a prescribed signal.
For example, in order to control a sheet conveying motor, a printer includes a disc-shaped scale, which has a plurality of slits arranged at prescribed distances therebetween, and a detector configured to include light emitting elements and light receiving elements with the slits interposed therebetween. This kind of scale rotates together with a conveying roller. In addition, this kind of detector generally outputs two rectangular-wave control signals whose phases are shifted from each other by 90° on the basis of detection signals output from the light receiving elements. The control signals are input to a prescribed controller that controls the printer. The controller controls a motor and the like on the basis of the two control signals. Such a technique is disclosed in Japanese Patent Publication No. 2001-232882A (JP-A-2001-232882), for example.
In recent years, in order to improve the printing quality, a motor or the like mounted in a printer is required to be controlled with high precision. In order to perform the high-precision control, it is necessary to output a signal with high resolution from an encoder. As a method of outputting a signal with high resolution from an encoder, two known methods may be considered. That is, one method is to enlarge the diameter of a disc-shaped scale while maintaining a distance between slits and the other method is to narrow the distance between slits while maintaining the diameter of the disc-shaped scale.
However, in the case of enlarging the diameter of a scale, such a scale is difficult to be disposed in a printer that is required to be downsized. Furthermore, in order to prepare a space for disposing the scale, the mechanical configuration of the printer becomes complicated. On the other hand, in the case of narrowing the distance between slits, it becomes difficult to manufacture the scale itself.